fix #77 Instant.toJson

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjInstant.kt

@@ -21,6 +21,8 @@ import kotlinx.datetime.Clock
 import kotlinx.datetime.Instant
 import kotlinx.datetime.isDistantFuture
 import kotlinx.datetime.isDistantPast
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonPrimitive
 import net.sergeych.lyng.Scope
 import net.sergeych.lynon.LynonDecoder
 import net.sergeych.lynon.LynonEncoder
@@ -89,6 +91,9 @@ class ObjInstant(val instant: Instant,val truncateMode: LynonSettings.InstantTru
         }
     }
 
+    override suspend fun toJson(scope: Scope): JsonElement = JsonPrimitive(instant.toString())
+
+
     companion object {
         val distantFuture by lazy {
             ObjInstant(Instant.DISTANT_FUTURE)